A hardware capable of displaying a 3D polygon with texture mapping and using semitransparent processing and fogging as special functions has been conventionally known. The semitransparent polygon processing is used, when a polygon is to be pictured, to exhibit such an effect of making an object model behind look through the polygon pictured by mixing a color data of a frame buffer and that of the polygon to be pictured at a desired rate for each pixel position. Further, fogging is used to exhibit such an effect of fogging an object by calculating a distance between an object model to be pictured and a viewing point of a simulated camera, setting a ratio of colors such that a mixture of these colors approaches a designated color according to the distance, and mixing these colors.
In photographing by a camera, a depth of field exists and objects more distant than the depth of field about a focusing position are blurred. If such a phenomenon is applied to a simulated 3D space such as a game space, a better presence of attendance can be provided. If it is applied to a video game, a better cubic effect can be provided and a possibility of providing a game using the presence of a depth of field can be given. However, this could not be realized by the conventional semitransparent processing and fogging.